Interpretive Summary: The southern cattle fever tick, Rhipicephalus (Boophilus) microplus, is a vector of Babesia bovis and B. bigemina, the single-celled organisms responsible for the often fatal disease commonly known as cattle fever. Although the Cattle Fever Tick Eradication Program (CFTEP) succeeded in eliminating cattle fever ticks (CFT) from the United States in 1943, these ticks remain endemic in Mexico. Populations of R. microplus in Mexico have evolved resistance to commercial acaricides. These ticks remain a threat to U.S. agriculture. New technologies are needed to keep the U.S. free of CFT in a sustainable manner. CFT are parasitic organisms that have to overcome host defense mechanisms to obtain blood for their survival. An understanding of the biological intricacies underlying CFT-cattle-pathogen interactions, including those involving the host immune system, is required to innovate technologies against CFT. Studies were conducted to investigate the effects of salivary gland extracts (SGE) from R. microplus on macrophages from cattle because these cells must regulate key co-stimulatory molecules on their cell surface to activate a protective immune response. R. microplus SGE specifically altered the expression of co-stimulatory molecules and suppressed markers of cell activation, which may facilitate successful tick feeding and promote pathogen transmission. These studies expand our knowledge of how bioactive factors in the salivary glands of R. microplus affect the ability of cattle to mount a successful immune response by altering the function of macrophages.

Technical Abstract:
The southern cattle fever tick, Rhipicephalus (Boophilus) microplus, is a vector of the apicomplexan protozoa Babesia bovis and B. bigemina, which cause the often fatal disease bovine babesiosis, also known as cattle fever. Although the Cattle Fever Tick Eradication Program (CFTEP) succeeded in eliminating cattle fever ticks (CFT) from the United States in 1943, these ticks remain endemic in Mexico. Populations of R. microplus in Mexico have evolved resistance to commercial acaricides. These ticks remain a threat to U.S. agriculture. New technologies are needed to keep the U.S. free of CFT in a sustainable manner. CFT are parasitic organisms that have to overcome host defense mechanisms to obtain blood for their survival. An understanding of the biological intricacies underlying CFT-cattle-Babesia interactions, including those involving the host immune system, is required to innovate technologies against CFT. Antigen presenting cells are central to the development of robust T cell responses including Th1 and Th2 determination. In this study we examined changes in co-stimulatory molecule expression and cytokine response of bovine macrophages exposed to salivary gland extracts (SGE) obtained from adult R. microplus. Molecules in the salivary glands of adult R. microplus showed bimodal concentration-, and time-dependent effects on differential up-regulation of CD86 in bovine macrophages activated by the TLR4-ligand, LPS. Pro-inflammatory cytokines and IL-12, a Th1 promoting cytokine, were down regulated in a dose-dependent manner. The co-stimulatory molecule CD80, as well as the cell activation marker, CD69, were also suppressed in macrophages exposed to SGE. These results indicate that molecules in the salivary glands of adult R. microplus evolved to affect the host’s ability to mount a successful immune response by altering co-stimulatory and activation marker expression in bovine macrophages. Continued investigation of the bioactive salivary factors will provide the knowledge base to research and develop therapeutic or prophylactic interventions targeting R. microplus-cattle interactions at the blood-feeding interface.